The present invention relates to extractors for removing broken threaded fasteners such as bolt studs from broken bolts, and more particularly to a broken fastener extractor combined with a drill head in a single combination tool.
The present invention is an improvement over my prior U.S. patent entitled "Easy-Out Threaded Fastener" filed Mar. 12, 1985 now U.S. Pat. No. 4,604,917.
Conventional easy out type bolt extractors for extracting broken bolt studs within a threaded bore are formed with gripping teeth and/or shaped flutes adapted to engage the sides of a previously drilled bore through the broken bolt stud. The gripping surfaces remove the threaded bolt stud when the extractor is rotated in a direction opposite to that of the bolt threads. These extractors require that first a hole be drilled through the broken bolt stud prior to the insertion of the extractor. A shortcoming of this tool is that the drill bit is often broken in the process of drilling which results in a compound problem of removal of both the broken bolt stud and the broken drill bit. Even when the drill bit is not broken, the bolt stud is often driven deeper into the threaded hole making extraction more difficult. This process requires that the drill bit be removed before inserting the bolt extractor so that at least three separate operations are needed using at least three separate tools including a drill bit, a tap wrench and extractor.
The present invention combines a drill for forming a bore within a broken bolt stud and bolt stud extractor for removing the broken bolt stud in a single tool. The lower portion of the tool is provided with a drill bit having a cutting edge threaded with a pitch in the direction opposite to the threads of the broken bolt stud being extracted and a drill body having a truncated surface which tapers outwardly toward the drill bit. The drill body is connected to a threaded shaft, the upper portion of which includes a drive head for a suitable hand or power driven tool. A bolt extractor collet is threadedly mounted on the drill bit shaft between the drill bit and the drive head portion of the tool.
To remove a broken bolt stud which remains within a threaded bore, the drill bit engages the broken bolt stud and driving of the drive head drills a hole within the body of the broken bolt stud. As the tool penetrates within the broken bolt stud, the extractor collet, which is threadedly mounted on the drill bit shaft, engages the interior of the hole being bored in the broken bolt stud. At that point, the drilling mode stops and the drill bit is rotated out of the bore toward the extractor collet by the reverse threads on the drill bit shaft. As the drill bit shaft and drill bit are driven outwardly from the bore, the interior surface of the extractor collet engages the truncated surface on the drill body causing a lower resilient portion of the extractor collet to expand outwardly to firmly grip the interior wall of the bore within the broken bolt stud. Because the extractor and the drill bit have been rotated together, they act as a single unit, and therefore, continued rotation of the tool will unthread the broken bolt stud to extract it.
Among the objects of the present invention are the provision of a threaded fastener extractor tool which is combined with a drilling bit so that a broken bolt stud may be removed in a single operation.